Lighting device

ABSTRACT

For integration of light-emitting elements and for suppression of a voltage drop, plural stages of light-emitting element units provided over a substrate having an insulating surface and each including a plurality of light-emitting elements which is connected in parallel are connected in series. Further, besides a lead wiring with a large thickness, a plurality of auxiliary wirings with different widths and different thicknesses is used, and the arrangement of the wirings, electrodes of the light-emitting elements, and the like is optimized. Note that in the lighting device, light emitted from the light-emitting element passes through the substrate having an insulating surface and then is extracted.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lighting device including alight-emitting member which exhibits electroluminescence (EL).

2. Description of the Related Art

Light-emitting elements containing organic compounds as light-emittingbodies have been expected to be applied to next-generation lighting.Light-emitting elements containing organic compounds as light-emittingbodies have features such as drive at a low voltage with low powerconsumption.

An EL layer included in a light-emitting element includes at least alight-emitting layer. In addition, the EL layer can have a layeredstructure including a hole injection layer, a hole transport layer, anelectron transport layer, an electron injection layer, and/or the like,in addition to the light-emitting layer.

It is said that, as for a light-emitting mechanism of a light-emittingelement, an EL layer is interposed between a pair of electrodes andvoltage is applied to the EL layer, so that electrons injected from acathode and holes injected from an anode are recombined in an emissioncenter of the EL layer to form molecular excitons, and the molecularexcitons release energy when returning to a ground state; thus, light isemitted. Singlet excitation and triplet excitation are known as excitedstates, and light emission can probably be achieved through either ofthe excited states.

Further, since the pair of electrodes and the light-emitting layer areformed as films in such a light-emitting element, surface light emissioncan easily be obtained by forming a large-area light-emitting element.This is a feature which is hard to obtain in light sources such asincandescent lamps and LEDs (point light sources) or in fluorescentlamps (line light sources), so that the above light-emitting element hasa high utility value as a light source such as lighting.

Patent Documents 1 and 2 disclose light-emitting devices in each ofwhich a plurality of light-emitting elements is connected in series.

REFERENCE

-   [Patent Document 1] Japanese Published Patent Application No.    2006-049853-   [Patent Document 2] Japanese Published Patent Application No.    2006-108651

SUMMARY OF THE INVENTION

An object of one embodiment of the present invention is to provide alighting device which is provided with a relatively large light-emittingregion by integration of a plurality of light-emitting elements, and amanufacturing method thereof.

Another object of one embodiment of the present invention is to providea lighting device which is thin and lightweight.

Another object of one embodiment of the present invention is to providea lighting device which can resist an impulse such as a drop impulse.

When a lighting device having a relatively large light-emitting regionis fabricated, one of a pair of electrode layers of a light-emittingelement is formed using a conductive material having alight-transmitting property. A conductive material having alight-transmitting property, such as indium tin oxide (hereinafterreferred to as ITO) has a resistance value larger than that of a metalmaterial used for a wiring layer, such as aluminum or titanium. Thus,when a conductive layer, a wiring, or the like is formed using aconductive material having a light-transmitting property, a voltage dropis likely to be caused. Note that a current path in a conductive layerincluding a material with a large resistance value has resistance in anycase, which leads to a voltage drop.

For integration of a plurality of light-emitting elements andsuppression of a voltage drop, the light-emitting elements are connectedin series, a plurality of auxiliary wirings with different widths anddifferent thicknesses is used, and the arrangement of the auxiliarywirings, electrodes, the light-emitting elements, and the like isoptimized.

One embodiment of the present invention is a lighting device includingplural stages of light-emitting element units; a first wiring in contactwith the first-stage light-emitting element unit of the plural stages oflight-emitting element units; and a second wiring in contact with thelast-stage light-emitting element unit of the plural stages oflight-emitting element units. The first-stage light-emitting elementunit includes at least a first light-emitting element and a secondlight-emitting element which are connected in parallel. Thelight-emitting element unit adjacent to the first-stage light-emittingelement unit includes at least a third light-emitting element and afourth light-emitting element which are connected in parallel. The firstlight-emitting element, the second light-emitting element, the thirdlight-emitting element, and the fourth light-emitting element eachinclude a first electrode layer with a light-transmitting property, anorganic compound-containing layer which is in contact with the firstelectrode layer, a second electrode layer with reflectivity which is incontact with the organic compound-containing layer, and an auxiliarywiring which is in contact with the first electrode layer and has anarrower width than the first wiring and the second wiring. The secondelectrode layer of the first light-emitting element and the auxiliarywiring of the third light-emitting element are connected to each other,whereby the first light-emitting element and the third light-emittingelement are connected in series. The second electrode layer of thesecond light-emitting element and the auxiliary wiring of the fourthlight-emitting element are connected to each other, whereby the secondlight-emitting element and the fourth light-emitting element areconnected in series. The auxiliary wiring of each of the light-emittingelements in the first-stage light-emitting element unit is in contactwith the first wiring. The second electrode layer of each of thelight-emitting elements in the last-stage light-emitting element unit isin contact with the second wiring.

Note that the number of stages of the light-emitting element units istwo or more, the light-emitting element unit in contact with the firstwiring is referred to as the first-stage light-emitting element unit,and the light-emitting element unit in contact with the second wiring isreferred to as the last-stage light-emitting element unit. For example,when the number of stages of the light-emitting element units is four,the first-stage light-emitting element unit is provided so as to beadjacent to the second-stage light-emitting element unit, thesecond-stage light-emitting element unit is provided so as to beadjacent to the third-stage light-emitting element unit, and thethird-stage light-emitting element unit is provided so as to be adjacentto the fourth-stage (last-stage) light-emitting element unit.

In one embodiment of the lighting device having the above structure, thethickness of each of the first wiring and the second wiring is greaterthan or equal to 3 μm and less than or equal to 30 μm, and the thicknessof the auxiliary wiring is greater than or equal to 0.1 μm and less than3 μm. The first wiring, the second wiring, and the auxiliary wiring eachinclude a conductive layer containing copper and have low resistance.The auxiliary wiring is provided in contact with the first electrodelayer having a light-transmitting property, whereby a voltage drop issuppressed.

With the above structure, the plurality of light-emitting elements canemit light efficiently or the total emission area can be increased.

Further, plural kinds of auxiliary wirings each having a smallerthickness and a narrower line width than the first wiring and the secondwiring may be provided. One embodiment of the present invention is alighting device including plural stages of light-emitting element unitsconnected in series; a first wiring in contact with the first-stagelight-emitting element unit of the plural stages of light-emittingelement units; and a second wiring in contact with the last-stagelight-emitting element unit of the plural stages of light-emittingelement units. The first-stage light-emitting element unit includes atleast a first light-emitting element and a second light-emitting elementwhich are connected in parallel. The light-emitting element unitadjacent to the first-stage light-emitting element unit includes atleast a third light-emitting element and a fourth light-emitting elementwhich are connected in parallel. The first light-emitting element, thesecond light-emitting element, the third light-emitting element, and thefourth light-emitting element each include a first electrode layer witha light-transmitting property, an organic compound-containing layerwhich is in contact with the first electrode layer, a second electrodelayer with reflectivity which is in contact with the organiccompound-containing layer, a first auxiliary wiring which is in contactwith the first electrode layer and has a narrower width than the firstwiring and the second wiring, and a second auxiliary wiring which is incontact with the first electrode layer and has a narrower width than thefirst auxiliary wiring. The second electrode layer of the firstlight-emitting element and the first auxiliary wiring of the thirdlight-emitting element are connected to each other, whereby the firstlight-emitting element and the third light-emitting element areconnected in series. The second electrode layer of the secondlight-emitting element and the first auxiliary wiring of the fourthlight-emitting element are connected to each other, whereby the secondlight-emitting element and the fourth light-emitting element areconnected in series. The first auxiliary wiring of each of thelight-emitting elements in the first-stage light-emitting element unitis in contact with the first wiring. The second electrode layer of eachof the light-emitting elements in the last-stage light-emitting elementunit is in contact with the second wiring.

In one embodiment of the lighting device having the above structure, thethickness of each of the first wiring and the second wiring is greaterthan or equal to 3 μm and less than or equal to 30 μm, the thickness ofthe first auxiliary wiring is greater than or equal to 0.1 μm and lessthan 3 μm, and the thickness of the second auxiliary wiring is greaterthan or equal to 3 nm and less than or equal to 30 nm. The first wiring,the second wiring, the first auxiliary wiring, and the second auxiliarywiring each include a conductive layer containing copper and have lowresistance. The first auxiliary wiring and the second auxiliary wiringare provided in contact with the first electrode layer having alight-transmitting property, whereby a voltage drop is suppressed.Although the second auxiliary wiring overlaps with a light-emittingregion of the light-emitting element, the total area of light emissionis less likely to be influenced by the second auxiliary wiring becausethe second auxiliary wiring has a smaller thickness and a narrower linewidth than the first auxiliary wiring.

In each of the light-emitting elements of one embodiment of the lightingdevice having the above structure, an insulating layer which is over andin contact with the first electrode layer and has an opening is providedand the organic compound-containing layer is in contact with the firstelectrode layer in the opening. The insulating layer is called apartition wall or a bank and prevents a short circuit between theadjacent light-emitting elements. The area of the opening formed in theinsulating layer, namely, the area of a region where the organiccompound-containing layer and the first electrode layer is in contactwith each other is equal to or substantially equal to the area of anemission region of one light-emitting element in a plan view.

One embodiment of the lighting device having the above structureincludes first plural stages of light-emitting element units and secondplural stages of light-emitting element units adjacent to the firstplural stages of light-emitting element units. The first plural stagesof light-emitting element units and the second plural stages oflight-emitting element units are arranged axisymmetrically with respectto the length direction of the second wiring in a plan view. Theplurality of light-emitting element units is provided axisymmetricallyand a plurality of wirings which is extended in the linear directioncorresponding to that of the symmetry axis and is given the samepotentials may be formed as one wiring, leading to a reduction in totalnumber of wirings.

In one embodiment of the lighting device having the above structure, thefirst light-emitting element and the second light-emitting element areconnected in parallel. The second electrode layer of the firstlight-emitting element is in contact with the first electrode layer ofthe third light-emitting element, whereby the first light-emittingelement and the third light-emitting element are connected in series.The second electrode layer of the second light-emitting element is incontact with the first electrode layer of the fourth light-emittingelement, whereby the second light-emitting element and the fourthlight-emitting element are connected in series. Serial connectionenables application of a higher voltage to the lighting device; thus,the load on a converter can be reduced.

In one embodiment of the lighting device having the above structure, theplural stages of light-emitting element units are provided over asubstrate having an insulating surface and functioning as a housing. Thesubstrate having an insulating surface has recessed portions in whichthe first wiring and the second wiring are provided in a plan view. Thefirst wiring and the second wiring are covered with a planarizationfilm.

In one embodiment of the lighting device having the above structure,light emitted from the first light-emitting element, the secondlight-emitting element, the third light-emitting element, and the fourthlight-emitting element passes through the substrate having an insulatingsurface and then is extracted. An optical member such as a microlensarray or a diffusion plate may be provided over the substrate having aninsulating surface as necessary to provide a large-area lighting devicecapable of more uniform light emission.

An inorganic insulating film (inorganic insulator) covering a topsurface of the light-emitting element is preferably provided to improvereliability. Further, an inorganic insulating film may be providedbetween an emission surface of the light-emitting element and thehousing. The inorganic insulating film serves as a sealing film or aprotective layer which blocks an external contaminant such as water. Theinorganic insulating film can be formed to have either a single-layerstructure or a layered structure using any of a nitride film and anitride oxide film. As the inorganic insulator, thin glass can be used.By providing the inorganic insulating film, deterioration of thelight-emitting element can be suppressed and the durability and thelifetime of the lighting device can be improved.

The shape of the emission surface of the light-emitting element may be acircular shape or a polygonal shape such as a quadrangle. The shape ofthe housing covering the light-emitting element may correspond to theshape of the emission surface and can be a rectangular solid, apolygonal cylinder, a cylinder, or the like.

Further, the EL layer may have a layered structure including two or morelayers provided with an intermediate layer laid therebetween. Bystacking a plurality of EL layers with different emission colors, anemission color to be provided can be controlled. By stacking a pluralityof EL layers even with the same emission color, an effect of improvingpower efficiency can be obtained.

Further, the EL layer may have a layered structure including, as one oflayers, a layer containing a composite material in which an acceptorsubstance is mixed with an organic compound having a high hole transportproperty. The layer containing a composite material is in contact withthe second electrode layer, whereby a short circuit of thelight-emitting element can be suppressed.

Note that in this specification, a lighting device refers to alight-emitting device or a light source (including lighting) andincludes a light-emitting element provided with at least alight-emitting layer between a pair of electrodes. Further, the lightingdevice includes the following modules in its category: a module in whicha connector such as a flexible printed circuit (FPC), a tape automatedbonding (TAB) tape, or a tape carrier package (TCP) is attached to alighting device; and a module having a TAB tape or a TCP provided with aconverter or the like at the end thereof.

According to one embodiment of the present invention, a lighting devicewhich is provided with a relatively large light-emitting region byintegration of a plurality of light-emitting elements and amanufacturing method thereof can be provided.

According to one embodiment of the present invention, a lighting devicewhich is thin and lightweight can be provided.

When plastic or a thin metal plate is used as a substrate used for alighting device, the lighting device can have resistance against animpulse such as a drop impulse.

In a lighting device according to one embodiment of the presentinvention, a plurality of light-emitting elements can emit lightefficiently or the total area of light emission can be increased.

According to one embodiment of the present invention, a lighting devicecan be formed by connecting a plurality of light-emitting element unitsof given stages in series or in series-parallel combination; thus, thelighting device can be increased in size. For example, it is possible torealize a lighting device whose emission region is one surface of alarge substrate with a size corresponding to G5.5 (1100 mm×1300 mm) toG11 (3000 mm×3300 mm) of the size of a mother glass substrate of aliquid crystal panel.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a plan view illustrating a lighting device;

FIGS. 2A and 2B are cross-sectional views illustrating a lightingdevice;

FIG. 3 is a plan view illustrating a lighting device;

FIGS. 4A and 4B are cross-sectional views illustrating a lightingdevice;

FIG. 5 is a plan view illustrating a lighting device;

FIGS. 6A and 6B are cross-sectional views each illustrating a lightingdevice;

FIG. 7 is a cross-sectional view illustrating a lighting device;

FIGS. 8A, 8B1, 8B2, and 8C are diagrams each illustrating an example ofa light-emitting element applicable to a lighting device;

FIG. 9 is a diagram illustrating examples of application of a lightingdevice;

FIG. 10 is a diagram illustrating an example of application of alighting device;

FIGS. 11A and 11B are cross-sectional views illustrating a lightingdevice;

FIGS. 12A and 12B are cross-sectional views each illustrating a lightingdevice; and

FIGS. 13A1 and 13A2 are a cross-sectional view and a plan viewillustrating a lighting device, respectively, and FIGS. 13B1 and 13B2are a cross-sectional view and a plan view illustrating a lightingdevice, respectively.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to theaccompanying drawings. Note that the present invention is not limited tothe description below, and it is easily understood by those skilled inthe art that a variety of changes and modifications can be made withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention should not be construed as being limited to thefollowing descriptions of the embodiments. In the structures to be givenbelow, the same portions or portions having similar functions aredenoted by the same reference numerals in different drawings, anddescriptions thereof will not be repeated.

Embodiment 1

In this embodiment, a lighting device according to an embodiment of thepresent invention will be described with reference to FIG. 1, FIGS. 2Aand 2B, FIG. 3, FIGS. 4A and 4B, FIG. 5, FIGS. 6A and 6B, FIG. 7, FIGS.11A and 11B, FIGS. 12A and 12B, and FIGS. 13A1, 13A2, 13B1, and 13B2.Note that common portions are denoted by the same reference numerals inFIG. 1, FIGS. 2A and 2B, FIG. 3, FIGS. 4A and 4B, FIG. 5, FIGS. 6A and6B, FIG. 7, FIGS. 11A and 11B, FIGS. 12A and 12B, and FIGS. 13A1, 13A2,13B1, and 13B2.

FIG. 1 is a plan view illustrating part of a lighting device accordingto this embodiment. FIG. 2A is a cross-sectional view along A1-A2 inFIG. 1, and FIG. 2B is a cross-sectional view along B1-B2 in FIG. 1.

FIG. 1 is the plan view of the lighting device in which a plurality oflight-emitting elements is arranged between a first wiring 124 and asecond wiring 128. In this embodiment, eight light-emitting elements areused for simplification; however, the number of the light-emittingelements is not particularly limited.

The first wiring 124 is a lead wiring which has a great line width and alarge thickness and is formed using a low resistance material. The firstwiring 124 is electrically connected to a power source (not illustratedhere), and current is supplied to each of the light-emitting elementsthrough the first wiring 124.

The second wiring 128 is a lead wiring which has a great line width anda large thickness and is formed using a low resistance material. Thesecond wiring 128 is given a fixed potential (also referred to as acommon potential).

The first wiring 124 and the second wiring 128 can also be referred toas main wirings and branch at a variety of positions. Note that a linewidth of a branching portion of the first wiring 124 is substantiallyequal to a line width of a branching portion of the second wiring 128.Although FIG. 1 illustrates an example in which the direction of theportions branching from one first wiring 124 is the same and the firstwiring has a comb-like shape, one embodiment of the present invention isnot particularly limited thereto. In a layout of the wiring, branchingportions thereof may be axisymmetrical with respect to the lengthdirection of the wiring (a layout of a lattice-like wiring), orbranching portions thereof may be alternately branched from the wiring.The first wiring 124 and the second wiring 128 are each preferablyformed to a thickness in the range of greater than or equal to 3 μm andless than or equal to 30 μm with the use of a low resistance material.For example, the first wiring 124 and the second wiring 128 are eachformed to have a single-layer structure or a layered structure using amaterial selected from aluminum (Al), titanium (Ti), tantalum (Ta),tungsten (W), molybdenum (Mo), chromium (Cr), neodymium (Nd), scandium(Sc), nickel (Ni), and copper (Cu) or an alloy material including any ofthese materials as its main component.

To form the first wiring 124 and the second wiring 128, platingtreatment (an electrolytic plating method or an electroless platingmethod) may be performed. As a metal material to be plated, a lowresistance material such as copper, silver, gold, chromium, iron,nickel, platinum, or an alloy thereof can be used.

In this embodiment, the first wiring 124 has a two-layer structure of atitanium layer and a copper layer over the titanium layer. A first layerand a second layer of the first wiring 124 are denoted by referencenumerals 124 a and 124 b, respectively, as in FIGS. 2A and 2B. Further,a first layer and a second layer of the second wiring 128 are denoted byreference numerals 128 a and 128 b, respectively. The first wiring 124and the second wiring 128 are provided with the insulating layer 103laid therebetween to keep a distance between the first wiring 124 andthe second wiring 128 so as not to be in contact with each other and notto cause a short circuit, as in FIG. 2B.

The insulating layer 103 can be formed using an inorganic insulatingmaterial or an organic insulating material. Note that an organicinsulating material having heat resistance, such as an acrylic resin, apolyimide, a benzocyclobutene-based resin, a polyamide, or an epoxyresin, is preferably used as a planarization insulating film. Other thansuch organic insulating materials, it is possible to use alow-dielectric constant material (a low-k material), a siloxane-basedresin, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), orthe like. The insulating layer 103 may be formed by stacking a pluralityof insulating films formed using any of these materials.

There is no particular limitation on the method for forming theinsulating layer 103, and the insulating layer 103 can be formed,depending on a material thereof, by a sputtering method, a spin coatingmethod, a dipping method, a printing method, an ink-jet method, or thelike.

As illustrated in FIG. 2A, the first wiring 124 is electricallyconnected to a first electrode layer 104 a 1 of a first light-emittingelement 132 a 1 through an auxiliary wiring 125 a 1. The firstlight-emitting element 132 a 1 includes the first electrode layer 104 a1, an EL layer 106 a 1, and a second electrode layer 108 a 1. Light fromthe EL layer 106 a 1 is emitted through the first electrode layer 104 a1 and a housing 100 to the outside; thus, an emission surface is on thefirst electrode layer 104 a 1 side. Accordingly, the first electrodelayer 104 a 1 and a housing 100 transmit at least light from the ELlayer 106 a 1.

As a material of the first electrode layer 104 a 1, indium oxide(In₂O₃), tin oxide (SnO₂), zinc oxide (ZnO), ITO, an indium oxide-zincoxide alloy (In₂O₃—ZnO), or any of these metal oxide materials in whichsilicon oxide is contained can be used. Alternatively, graphene may beused as a material of the first electrode layer 104 a 1.

The first wiring 124 is electrically connected to a first electrodelayer 104 a 2 of a second light-emitting element 132 a 2 through anauxiliary wiring 125 a 2.

In this embodiment, eight light-emitting elements are categorized intoplural stages of light-emitting element units for simplification.

The first light-emitting element 132 a 1 and the second light-emittingelement 132 a 2 are collectively referred to as a first-stagelight-emitting element unit 133 a 1. The plurality of light-emittingelements in the first-stage light-emitting element unit 133 a 1 isconnected in parallel.

Current from the power source is supplied to the EL layer 106 a 1through the first wiring 124, the auxiliary wiring 125 a 1, and thefirst electrode layer 104 a 1. The second electrode layer 108 a 1electrically connected to the EL layer 106 a 1 is electrically connectedto the auxiliary wiring 125 a 3.

The second electrode layer 108 a 1 is preferably formed using a metalhaving a low work function (typically, a metal element which belongs toGroup 1 or Group 2 of the periodic table), or an alloy thereof.Specifically, aluminum or an aluminum alloy is used for the secondelectrode layer 108 a 1. However, when aluminum or an aluminum alloy isprovided in direct contact with ITO or the like, the aluminum or thealuminum alloy might possibly be corroded. Therefore, in thisembodiment, the second electrode layer 108 a 1 of the firstlight-emitting element 132 a 1 is not provided in direct contact withthe first electrode layer 104 a 3 of the third light-emitting element132 a 3 serially connected to the first light-emitting element 132 a 1,but is connected to the first electrode layer 104 a 3 through theauxiliary wiring 125 a 3.

The auxiliary wiring 125 a 3 can be formed to have a single-layerstructure or a layered structure using a material such as copper (Cu),titanium (Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium(Cr), neodymium (Nd), scandium (Sc), or nickel (Ni) or an alloy materialcontaining any of these materials as its main component. Aluminum may beused as a material of the auxiliary wiring 125 a 3. When aluminum isused as a material of the auxiliary wiring 125 a 3, a layered structurein which aluminum is used as a layer not in contact with ITO or the likemay be employed so that the problem of corrosion described above is notcaused. The auxiliary wiring 125 a 3 has a narrower line width and asmaller thickness than the first wiring and the second wiring.Specifically, the thickness of the auxiliary wiring 125 a 3 is greaterthan or equal to 0.1 μm and less than 3 μm.

Further, the second-stage light-emitting element unit, the last-stagelight-emitting element unit 133 a 2 in this embodiment, is provided soas to be adjacent to the first-stage light-emitting element unit 133 a1.

The last-stage light-emitting element unit 133 a 2 includes the thirdlight-emitting element 132 a 3 serially connected to the firstlight-emitting element 132 a 1 in the first-stage light-emitting elementunit 133 a 1.

In FIG. 2A, the plurality of light-emitting elements is connected inseries. The auxiliary wiring 125 a 3 is electrically connected to thefirst electrode layer 104 a 3 of the third light-emitting element 132 a3. The first electrode layer 104 a 3 is electrically connected to an ELlayer 106 a 3. The second electrode layer 108 a 3 electrically connectedto the EL layer 106 a 3 is electrically connected to the second wiring128.

Further, as illustrated in FIG. 2A, in the lighting device, aninsulating layer 135 which is over and in contact with the firstelectrode layers and has openings is provided, and the EL layers are incontact with the first electrode layers in the openings. The insulatinglayer 135 prevents a short circuit between the adjacent light-emittingelements. As illustrated in FIG. 2B, the insulating layer 135 isprovided between the plurality of light-emitting elements which isadjacent to each other and connected in parallel, and end portions ofthe EL layers are located over the insulating layer 135. In addition, asillustrated in FIG. 2B, end portions of the second electrode layers arelocated over the insulating layer 135 provided between the plurality oflight-emitting elements which is adjacent to each other and connected inparallel. Further, as illustrated in FIG. 2B, the plurality oflight-emitting elements is connected in parallel, and as illustrated inFIG. 2A, an inorganic insulating film 140 is in contact with theinsulating layer 135 between the plurality of light-emitting elementswhich is adjacent to each other.

The insulating layer 135 is formed using an organic insulating materialsuch as a polyimide, acrylic, a polyamide, or epoxy, or an inorganicinsulating material. It is particularly preferable that the insulatinglayer 135 be formed using a photosensitive resin material to haveopenings over the first electrode layers so that sidewalls of theopenings are formed to have tilted surfaces with continuous curvature.

Note that the second electrode layers 108 a 2 and 108 a 3 can be formedusing a material and a manufacturing process which are similar to thoseof the second electrode layer 108 a 1. The auxiliary wirings 125 a 1 and125 a 2 can be formed using a material and a manufacturing processsimilar to those of the auxiliary wiring 125 a 3 described above.

The last-stage light-emitting element unit 133 a 2 includes a fourthlight-emitting element 132 a 4 serially connected to the secondlight-emitting element 132 a 2 in the first-stage light-emitting elementunit 133 a 1.

The light-emitting element unit connected to and in contact with thesecond wiring 128 is the last-stage light-emitting element unit 133 a 2.

Further, as illustrated in FIG. 1, the first wiring 124 branches at twopositions to have protruding portions, and the second wiring 128branches at one position to have a protruding portion. In FIG. 1, theprotruding portions are provided in comb-like shapes.

Furthermore, in FIG. 1, the protruding portions branching from the twopositions of the first wiring 124 are parallel to or substantiallyparallel to each other and also parallel to the protruding portionbranching from the one position of the second wiring 128. Thefirst-stage light-emitting element unit 133 a 1 and the last-stagelight-emitting element unit 133 a 2, that is, the first to the fourthlight-emitting elements are provided between the protruding portionbranching from the first position of the two position of the firstwiring 124, and the protruding portion branching from the one positionof the second wiring 128.

It is also a feature of this embodiment that the protruding portionbranching from the one position which is a part of the second wiring 128is straight in the length direction, and a layout is axisymmetric withrespect to the straight line as a symmetry axis. In FIG. 1, a straightline 170 corresponds to the symmetry axis.

A first-stage light-emitting element unit 133 b 1 and a last-stagelight-emitting element unit 133 b 2, that is, the fifth to the eighthlight-emitting elements are provided between the protruding portionbranching from the second position of the two positions of the firstwiring 124, and the protruding portion branching from the one positionof the second wiring 128.

The protruding portion branching from the one position of the secondwiring 128 is provided between the last-stage light-emitting elementunit 133 a 2 and the last-stage light-emitting element unit 133 b 2. Inthis manner, the plurality of light-emitting element units is providedaxisymmetrically and a plurality of wirings whose length directioncorresponds to that of the symmetry axis and which is given the samepotentials is formed as one wiring, leading to a reduction in totalnumber of wirings.

Note that the inorganic insulating film 140 covering a top surface ofthe light-emitting element 132 is preferably provided. In addition, aninorganic insulator 102 may be provided between the emission surface ofthe light-emitting element 132 and a housing 100. The inorganicinsulating film 140 and the inorganic insulator 102 function asprotective layers or sealing films which block an external contaminantsuch as water. By providing the inorganic insulating film 140 and theinorganic insulator 102, deterioration of the light-emitting element 132can be suppressed and thus, the durability and the lifetime of thelighting device can be increased.

As each of the inorganic insulating film 140 and the inorganic insulator102, a single layer or a stack using a nitride film and a nitride oxidefilm can be used. Specifically, the inorganic insulating film 140 andthe inorganic insulator 102 can be formed using silicon oxide, siliconnitride, silicon oxynitride, aluminum oxide, aluminum nitride, aluminumoxynitride, or the like by a CVD method, a sputtering method, or thelike depending on the material. The inorganic insulating film 140 andthe inorganic insulator 102 are preferably formed using silicon nitrideby a CVD method. The thickness of the inorganic insulating film may beapproximately 100 nm to 1 μm.

Alternatively, as each of the inorganic insulating film 140 and theinorganic insulator 102, an aluminum oxide film, a diamond like carbon(DLC) film, a carbon film containing nitrogen, or a film containing zincsulfide and silicon oxide (e.g., a ZnS.SiO₂ film) may be used.

As the inorganic insulator 102, a thin glass substrate can be used. Forexample, a glass substrate with a thickness in the range of greater thanor equal to 30 μm and less than or equal to 100 μm can be used.

When a glass substrate or the like is used for the inorganic insulator102, entry of moisture, an impurity, or the like into an organiccompound and a metal material which are contained in the light-emittingelement from the outside of the lighting device can be suppressed.Consequently, deterioration of the light-emitting element due tomoisture, an impurity, or the like can be suppressed, leading toimprovement in reliability of the lighting device. In addition, thelighting device can have resistance against bending and breaking, and areduction in weight of the lighting device can be achieved because theglass substrate has a small thickness, a thickness in the range ofgreater than or equal to 30 μm and less than or equal to 100 μm.

As specific examples of a member used for the housing 100, plastic (anorganic resin), glass, quartz, and the like can be given. As an exampleof plastic, a member made of polycarbonate, polyarylate,polyethersulfone, or the like can be given. It is preferable to useplastic for the housing 100 because a reduction in weight of thelighting device can be achieved. In addition, the lighting device canhave resistance against an impulse such as a drop impulse when plasticis used for the housing 100.

FIG. 1 and FIGS. 2A and 2B illustrate an example in which the auxiliarywirings each having a smaller thickness and a narrower line width thanthe first wiring and the second wiring is provided; however, auxiliarywirings each having a narrower line width and a smaller thickness(specifically, greater than or equal to 3 nm and less than or equal to30 nm) than the auxiliary wiring may be provided in addition to theauxiliary wirings.

FIG. 3 is a plan view where auxiliary wirings each having a smallthickness is provided. Note that FIG. 4A is a cross-sectional view alongA1-A2 in FIG. 3, and FIG. 4B is a cross-sectional view along B1-B2 inFIG. 3. A structure except for the auxiliary wirings each having a smallthickness is the same as that of FIG. 1 and FIGS. 2A and 2B; thus,specific description thereof is omitted here.

FIG. 3 illustrates an example in which auxiliary wirings 126 whosepattern shapes are mesh-like shapes are provided. As in FIG. 3, theauxiliary wirings 126 are provided in contact with the auxiliary wirings125 and are electrically connected to the auxiliary wirings 125. As inFIG. 3 and FIGS. 4A and 4B, the auxiliary wirings 126 are formed incontact with the first electrode layers 104 and are located to overlapwith light-emitting regions. The auxiliary wirings 126 each having asmaller thickness and a narrower line width than the auxiliary wiring125 is less likely to influence the total area of light emission.Although FIGS. 4A and 4B illustrate an example in which the auxiliarywirings 126 are provided over the insulating layer 103, the auxiliarywirings 126 may be provided over the first electrode layers 104.

The use of a material such as copper for formation of the auxiliarywiring 126 can suppress a voltage drop when the first electrode layer104 has a large area. The material of the second auxiliary wiring is notlimited to copper and may be the same as a material of the auxiliarywiring 125.

The pattern shape of the auxiliary wiring 126 is not limited to amesh-like shape but may be a stripe shape. It is preferable that thepattern shape, the width, and the thickness of the auxiliary wiring 126and the resistivity of a material of the auxiliary wiring 126 beadjusted as appropriate depending on the shape and the area of the firstelectrode layer 104 by a practitioner so that a voltage drop issuppressed as much as possible.

In the cases of the structures in FIG. 1, FIGS. 2A and 2B, FIG. 3, andFIGS. 4A and 4B, the first wiring, the second wiring, the auxiliarywiring (or the second auxiliary wiring), and the first electrode layercan be formed through a photolithography process. The EL layer can beformed using a deposition mask, and a pattern of the second electrodelayer can also be formed using a deposition mask.

When a glass substrate having a large area, e.g., an area of 720 mm×600mm or an area of 750 mm×620 mm, is used for the housing 100, a layout inFIG. 5 is possible. FIG. 5 illustrates an example in which a pluralityof light-emitting elements is efficiently arranged over a glasssubstrate having a large area with the use of the structure in FIG. 3.

A block A includes a first wiring 124A branching at a plurality ofpositions, a second wiring 128A, and plural stages of light-emittingunits between the first wiring 124A and the second wiring 128A.

A block B includes a first wiring 124B branching at a plurality ofpositions, a second wiring 128B, and plural stages of light-emittingunits between the first wiring 124B and the second wiring 128B.

A block C includes a first wiring 124C branching at a plurality ofpositions, a second wiring 128C, and plural stages of light-emittingunits between the first wiring 124C and the second wiring 128C.

It is needless to say that the block A, the block B, and the block Chave the same patterns. Further, converters are illustrated in FIG. 5; afirst converter 160A, a second converter 160B, and a third converter160C are provided in the block A, the block B, and the block C,respectively, to form one large lighting device. Note that the structurein FIG. 5 is only an example; thus, the number of blocks is not limitedto that of the structure in FIG. 5. For example, the number of blocksmay be five.

In the cases of the structures in FIG. 1, FIGS. 2A and 2B, FIG. 3, andFIGS. 4A and 4B, a photomask is used and exposure is performed in aphotolithography process. For example, when a glass substrate with asize of 720 mm×600 mm is used and an exposure apparatus which can exposean area of 310 mm×560 mm to one shot of light, it is preferable toperform exposure of the block A, the block B, and the block C, which areillustrated in FIG. 5, to a first shot of light, a second shot of light,and a third shot of light, respectively, for efficient exposure. Notethat it is needless to say that the size of an area which can be exposedto one shot of light can be changed by optical adjustment, and thepositions to be exposed are adjusted so that a region to be exposed toone shot of light does not overlap with a region to be exposed toanother shot of light.

In the layout of FIG. 5, branching main wirings like costae are providedand the main wirings each have first auxiliary wirings like lateralveins. This state is like a state of a leaf having plural veins withdifferent thicknesses. Further, the first auxiliary wiring has secondauxiliary wirings which are extremely thin. It can be said that in thewiring layout in FIG. 5, the plural wirings with different thicknessesefficiently supply current from a power source to a plurality oflight-emitting elements, like plural veins with different thicknesses ofa leaf.

Note that in the lighting device described in this embodiment, thelight-emitting element 132 may be provided in a housing. In that case,the housing for sealing the light-emitting element 132 may be acombination of a plurality of housings attached to each other. Forexample, another housing is provided to face the housing 100 so that thelight-emitting element 132 is encapsulated, which enables sealing of thelight-emitting element 132. The housing provided opposite to the housing100 can be formed using a material similar to that of the housing 100.

Further, as illustrated in FIG. 7, a top surface of the light-emittingelement 132 may be provided with a metal plate 111 opposite to thehousing 100. There is no particular limitation on the thickness of themetal plate 111; however, the metal plate with a thickness in the rangeof greater than or equal to 10 μm and less than or equal to 200 μm ispreferably used because a reduction in weight of the lighting device canbe achieved. A material of the metal plate 111 is not limited to aparticular material, but it is preferable to use a metal such asaluminum, copper, or nickel, an alloy such as an aluminum alloy orstainless steel, or the like.

The metal plate 111 and the housing 100 are attached to each other withan adhesive layer 134, so that the light-emitting element 132 can besealed in. As the adhesive layer 134, a visible light curable adhesive,a UV curable adhesive, or a thermosetting adhesive can be used. Asexamples of materials of such adhesives, an epoxy resin, an acrylicresin, a silicone resin, a phenol resin, and the like can be given. Amoisture-absorbing substance serving as a drying agent may be containedin the adhesive layer 134.

Since the metal plate 111 has low permeability, sealing of thelight-emitting element 132 with the metal plate 111 and the housing 100can prevent entry of moisture into the light-emitting element 132. Thus,by providing the metal plate 111, a highly reliable lighting device inwhich deterioration due to moisture is suppressed can be obtained.

An inorganic insulating film, a glass substrate, a quartz substrate, orthe like may be used instead of the metal plate 111.

A moisture-absorbing substance serving as a drying agent may be providedin a space where the light-emitting element 132 is provided. Themoisture-absorbing substance may be placed as a solid such as a powderysubstance or may be provided as a film containing a moisture-absorbingsubstance over the light-emitting element 132 by a deposition methodsuch as a sputtering method.

The shape of the emission surface of the light-emitting element 132 maybe a circular shape or a polygonal shape such as a quadrangle, and theshape of the housing covering the emission surface may correspond to theshape of the emission surface.

Further, a plurality of light-emitting elements having differentemission colors is provided and connected to an external power sourceindividually to control a current value and a voltage value, so thatlight emission color from the lighting device can be adjusted and colorrendering properties thereof can be improved.

FIGS. 6A and 6B are examples of cross-sectional views of lightingdevices incorporating converters. Note that a converter refers to aconstant current power source which converts input power into a constantcurrent suited to specifications of a lighting device and supplies theconstant current to the lighting device, or a converter circuitfunctioning as a constant voltage power source which converts inputpower into a constant voltage suited to specifications of a lightingdevice and supplies the constant voltage to the lighting device.

The lighting device in FIG. 6A is connected to a converter 160 through aterminal electrode 164. In FIG. 6A, the terminal electrode 164 has alayered structure of a first layer 164 a and a second layer 164 b. Theterminal electrode 164 can be formed in the same step as the firstwiring 124 and the second wiring 128. In the lighting device in FIG. 6A,the light-emitting element 132 is sealed with the housing 100, a housing168, and a sealant 162. For the housing 168 opposite to the housing 100,a metal plate, a material similar to that of the housing 100, or thelike can be used.

The first electrode layer 104 and the second electrode layer 108 whichare included in the light-emitting element 132 are electricallyconnected to the converter 160, and a current suited to specificationsof the lighting device, which is obtained by conversion in the converter160, is supplied to the light-emitting element 132. Since current issupplied from both sides of the light-emitting element to thelight-emitting element, luminance unevenness can be reduced andconcentration of a load to part of the light-emitting element can besuppressed.

Note that it is preferable that a wiring for connecting the converter160 overlap with a non-light-emitting region of the lighting device inorder not to reduce light extraction efficiency of the lighting device.The converter 160 may be provided so as to protrude to be higher than aregion sealed with the sealant 162 as in FIG. 6B. Alternatively, theconverter 160 is not provided over the housing 100 and may be providedexternally.

As illustrated in FIG. 6B, a region between the inorganic insulatingfilm 140 and the housing 168 may be filled with a resin 151. As theresin 151, an epoxy resin, an acrylic resin, a silicone resin, a phenolresin, or the like can be used. Filling of the region between theinorganic insulating film 140 and the housing 168 with the resin 151allows the lighting device to withstand the weight of an object when theobject is placed over the housing 168.

In FIGS. 6A and 6B, the converter 160 is a DC-DC converter and includesa printed circuit board (not illustrated). When a printed circuit boardis used, insulation of a connection surface between the printed circuitboard and a terminal electrode is ensured, which facilitates alignmentin provision of the printed circuit board over the terminal electrode.As the printed circuit board, a flexible printed circuit board (FPC) ora semi-flexible printed circuit board partly having flexibility may beused. When a flexible printed circuit board is used, a converter can beincorporated in a flexible lighting device or a lighting device having acurved surface.

Note that a circuit element provided in the converter 160 may be formedso as to be embedded in the insulating layer 103 in order to prevent thethickness of the lighting device from increasing when the converter 160is provided over the terminal electrode.

As described above, when a converter is incorporated in a lightingdevice, a malfunction in which overcurrent flows to a light-emittingelement can be prevented owing to a function of supplying a stablecurrent suited to an element even if an input voltage varies. Further, alighting device which is usable even without an external converter canbe provided, so that the utilization range of lighting devices iswidened. Furthermore, provision of a converter or a connection wiringover a non-light-emitting region enables suppression of a decrease inarea of a light-emitting region; thus, a lighting device with highilluminance can be provided.

Note that a converter included in the lighting device according to thisembodiment is not limited to a DC-DC converter and may be an AC-DCconverter which converts AC voltage into DC voltage. When an AC-DCconverter is used, an AC power supply can be applied without conversion.Further, the number of light-emitting elements electrically connected toone converter in the lighting device according to this embodiment is notlimited to that of the structure described in this embodiment.

As illustrated in FIGS. 11A and 11B, the first wirings 124 (124 a and124 b) and the second wirings 128 (128 a and 128 b) may be provided soas to be embedded in recessed portions of the housing 100.

The recessed portions of the housing 100 may be formed by etching or byprocessing an organic resin with a supporter serving as a mold so thatthe organic resin has depressions and projections.

In the case where the inorganic insulator 102 is provided over thehousing 100 having the recessed portions, the inorganic insulator 102may be formed over the housing 100, and then the auxiliary wirings maybe formed over the inorganic insulator 102 so as to fill the recessedportion of the housing 100.

An optical film may be provided on the emission surface side of thelighting device. For example, the housing 100 may be provided with adiffusion film in a region which covers the emission surface and isopposite to the light-emitting element 132 side. Further, to increaseextraction efficiency, a lens array overlapping with the plurality oflight-emitting elements 132 may be provided on the emission surfaceside.

FIGS. 12A and 12B are examples of using housings 241 and 242 each havingan uneven shape including a plurality of projections like the shape of amicrolens array on the emission surface side (the side opposite to thelight-emitting element 132 side). When any of the structures of thehousings 241 and 242 each having an uneven shape including a pluralityof projections is used as the structure of the housing 100, totalreflection at the interface between the air and the housing 241/242 canbe suppressed; thus, the efficiency of light extraction to the outsideof the housing can be improved.

Further, provision of such a housing having an uneven shape allowsdiffusion of light of a light-emitting element, which is emitted to theoutside; thus, even adverse effects caused when a light-blockingauxiliary wiring is provided over the emission surface can be reduced.Accordingly, a lighting device can emit light uniformly and favorably.

The housing 241 having an uneven shape can be formed using an organicresin as its material. The organic resin can be processed by heattreatment or light irradiation treatment depending on characteristics ofthe organic resin. For example, a support having an uneven shape andserving as a mold of the uneven shape of the housing is prepared, athermoplastic organic resin is used as the material of the housing, thethermoplastic organic resin is pressed in the support while performingheat treatment so that the shape of the thermoplastic organic resin ischanged to reflect the shape of the support, and then the thermoplasticorganic resin is cured by cooling; thus, the housing 241 having anuneven shape can be formed.

As a specific example of a member used for the housing 241, an organicresin (plastic) is given. As an example of plastic, a member made ofpolycarbonate, polyarylate, polyethersulfone, or the like is given.

FIGS. 13A1, 13A2, 13B1, and 13B2 illustrate cross-sectional views andplan views of the housing 241 in FIG. 12A. FIGS. 13A2 and 13B2illustrate examples of plan views of housings 241 a and 241 b eachhaving an uneven shape. FIG. 13A1 is a cross-sectional view along X1-Y1in FIG. 13A2 and FIG. 13B1 is a cross-sectional view along X2-Y2 in FIG.13B2.

The housing 241 a illustrated in FIGS. 13A1 and 13A2 has an uneven shapein which a projection has a semispherical shape. The housing 241 billustrated in FIGS. 13B1 and 13B2 has an uneven shape in which the baseof a projection is a regular hexagon. The pitch or the bottom shape ofthe plurality of projections included in the housing 241 can be setvariously and is not limited to the structures in FIGS. 13A1, 13A2,13B1, and 13B2. For example, the housing 121 a may have an uneven shapewith an apex, such as a circular cone or a pyramid (e.g., a triangularpyramid or a square pyramid). Note that it is preferable to employ aso-called honeycomb structure for an uneven shape in which the base of aprojection is a regular hexagon as illustrated in FIGS. 13B1 and 13B2because the density of arrangement of the uneven shape can be improvedand the extraction efficiency of light to the outside of the housing canbe further improved.

Further, as illustrated in FIG. 12B, the housing 242 having an unevenshape including a plurality of projections, like a microlens array, maybe used on both the emission surface side (on the side opposite to thelight-emitting element 132) and the light-emitting element 132 side.

The housing 242 illustrated in FIG. 12B has uneven shapes each includinga plurality of projections on both sides. Further, in FIG. 12B, theuneven shape including a plurality of projections provided on thelight-emitting element 132 side overlap with the light-emitting element132. A high refractive index material layer 235 is provided in a regionhaving the uneven shape on the light-emitting element 132 side withrespect to the housing 242, so as to be in contact with the unevenshape. Note that the uneven shape provided on the housing 242 isarranged in a stripe shape, which is effective, but is preferablyarranged in a matrix shape.

The housing 242 illustrated in FIG. 12B has the uneven shape including aplurality of projections on the emission surface side of the housing242, whereby total reflection at the interface between the housing 242and the air can be suppressed. Moreover, the uneven shape including aplurality of projections is provided between the housing 242 and thehigh refractive index material layer 235, whereby total reflection atthe interface between the high refractive index material layer 235 andthe housing 242 can be suppressed and the extraction efficiency of lightto the outside of the housing can be further improved.

As examples of a material that can be used for the housing 242, glass, aresin, and the like whose refractive index is greater than 1.0 and lessthan 1.6 are given. As the resin, a polyester resin, a polyacrylonitrileresin, a polyimide resin, a polymethyl methacrylate resin, apolycarbonate resin, a polyethersulfone resin, a polyamide resin, acycloolefin resin, a polystyrene resin, a polyamide imide resin, apolyvinylchloride resin, or the like can be used. In particular, amaterial whose refractive index is greater than or equal to 1.4 and lessthan 1.6 is preferably used.

As a method for forming an uneven shape in the above material, forexample, an etching method, a sand blasting method, a microblastprocessing method, a droplet discharge method, a printing method (screenprinting or offset printing by which a pattern is formed), a coatingmethod such as a spin coating method, a dipping method, a dispensermethod, an imprint method, a nanoimprint method, or the like can beemployed as appropriate.

The high refractive index material layer 235 is formed of highrefractive index glass, a high refractive index liquid, or a highrefractive index resin. The high refractive index material layer 235 hasa light-transmitting property and the refractive index is greater thanor equal to 1.6, preferably greater than or equal to 1.7 and less thanor equal to 2.1. As examples of the high refractive index glass, a resincontaining bromine, a resin containing sulfur, and the like are given.For example, a sulfur-containing polyimide resin, an episulfide resin, athiourethane resin, a brominated aromatic resin, or the like can beused. Alternatively, polyethylene terephthalate (PET), triacetylcellulose (TAC), or the like may be used. As the high refractive indexliquid, a contact liquid (refractive liquid) containing sulfur andmethylene iodide, or the like can be used. Any of a variety of methodssuitable for the material may be employed for forming the highrefractive index material layer 235. For example, the above resin isselectively formed in contact with the uneven shape including aplurality of projections provided on the light-emitting element 132 sideof the housing 242 by a spin coating method and is cured by heat orlight, so that the high refractive index material layer 235 can beformed. The material and the deposition method can be selected asappropriate in consideration of the adhesion strength, ease ofprocessing, or the like. Note that the high refractive index materiallayer 235 also functions as a planarization film for the uneven shapeincluding a plurality of projections provided on the light-emittingelement 132 side of the housing 242.

In general, a resin with a high refractive index is expensive, but inthe lighting device illustrated in FIG. 12B, the high refractive indexmaterial layer 235 may be selectively formed in a region overlappingwith the light-emitting element 132 and in contact with the uneven shapeincluding a plurality of projections, and the thickness of the highrefractive index material layer 235 is several tens of micrometers,which is small. Thus, the lighting device with high light extractionefficiency can be manufactured at low cost.

The size and the height of the projection of the uneven shape on theside which is in contact with the high refractive index material layer235 are each preferably approximately 0.1 μm to 100 μm. The size and theheight of the projection of the uneven shape on the opposite side areeach preferably approximately 0.1 μm to 1000 μm. The size of theprojection of the uneven shape on the side which is in contact with thehigh refractive index material layer 235 affects the amount of materialused for the high refractive index material layer 235; thus, theallowable range of the size and the height of the projection is narrow.In contrast, the projection included in the uneven shape on the oppositeside may have a size or height exceeding 1000 μm. In particular, each ofthe projections included in the uneven shapes on both sides preferablyhave a size or height of greater than or equal to 1 μm because aninfluence of interference of light can be suppressed.

Further, in FIG. 12B, the high refractive index material layer 235 isprovided between the light-emitting element 132 and the housing 242.When a nitride film with a refractive index in the range of greater thanor equal to 1.6 is used as the high refractive index material layer 235,diffusion of impurities to the light-emitting element can be preventedwithout a decrease in the extraction efficiency of light, which ispreferable.

According to one embodiment of the present invention, a lighting devicecan be formed by connecting a plurality of light-emitting element unitsof given stages in series or in series-parallel combination; thus, thelighting device can be increased in size. For example, it is possible torealize a lighting device whose emission region is one surface of alarge substrate with a size corresponding to G5.5 (1100 mm×1300 mm) toG11 (3000 mm×3300 mm) of the size of a mother glass substrate of aliquid crystal panel.

Further, the lighting device according to this embodiment can be thinand lightweight.

When plastic or a thin metal plate is used for a substrate, a lightingdevice which can resist an impulse such as a drop impulse can beprovided.

In the lighting device according to this embodiment, the plurality oflight-emitting elements can emit light efficiently or the total emissionarea can be increased.

Embodiment 2

In this embodiment, an example of an element structure of alight-emitting element exhibiting organic EL emission, which is used ina lighting device according to one embodiment of the present invention,will be described. The light-emitting element exhibiting organic ELemission generates a smaller amount of heat than an LED. Thus, anorganic resin can be used for a housing, so that a reduction in weightof the lighting device is possible, which is preferable.

The light-emitting element illustrated in FIG. 8A includes the firstelectrode layer 104, an EL layer 106 over the first electrode layer 104,and the second electrode layer 108 over the EL layer 106.

The EL layer 106 includes at least a light-emitting layer containing alight-emitting organic compound. In addition, the EL layer 106 can havea layered structure in which a layer containing a substance having ahigh electron transport property, a layer containing a substance havinga high hole transport property, a layer containing a substance having ahigh electron injection property, a layer containing a substance havinga high hole injection property, a layer containing a bipolar substance(a substance having a high electron transport property and a high holetransport property), and the like are combined as appropriate. In thisembodiment, a hole injection layer 701, a hole transport layer 702, alight-emitting layer 703, an electron transport layer 704, and anelectron injection layer 705 are stacked in this order from the firstelectrode layer 104 side in the EL layer 106.

A method for manufacturing the light-emitting element illustrated inFIG. 8A will be described.

First, the first electrode layer 104 is formed. The first electrode 104is provided in the direction in which light is extracted from the ELlayer, and thus is formed using a light-transmitting material.

As the light-transmitting material, indium oxide, ITO, an indiumoxide-zinc oxide alloy (also referred to as IZO (registered trademark)),zinc oxide, zinc oxide to which gallium is added, graphene, or the likecan be used.

As the first electrode layer 104, a metal material such as gold,platinum, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper,palladium, or titanium can be used. Alternatively, a nitride of themetal material (such as titanium nitride), or the like may be used. Inthe case of using the metal material (or the nitride thereof), the firstelectrode layer 104 may be thinned so as to be able to transmit light.

Next, the EL layer 106 is formed over the first electrode layer 104. Inthis embodiment, the EL layer 106 includes the hole injection layer 701,the hole transport layer 702, the light-emitting layer 703, the electrontransport layer 704, and the electron injection layer 705.

The hole injection layer 701 is a layer containing a substance having ahigh hole injection property. As the substance having a high holeinjection property, for example, a metal oxide such as molybdenum oxide,titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromiumoxide, zirconium oxide, hafnium oxide, tantalum oxide, silver oxide,tungsten oxide, or manganese oxide can be used. A phthalocyanine-basedcompound such as phthalocyanine (abbreviation: H₂Pc) or copper(II)phthalocyanine (abbreviation: CuPc) may be used.

Further, any of the following aromatic amine compounds which are lowmolecular organic compounds can be used:4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2), and3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1).

Still alternatively, any of high molecular compounds (e.g., oligomers,dendrimers, or polymers) may be used. Examples of the high-molecularcompound include poly(N-vinylcarbazole) (abbreviation: PVK),poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD). A high molecular compound to which acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS)or polyaniline/poly(styrenesulfonic acid) (PAni/PSS), may be used.

In particular, for the hole injection layer 701, a composite material inwhich an organic compound having a high hole transport property is mixedwith an acceptor substance is preferably used. With the use of thecomposite material in which an organic compound having a high holetransport property is mixed with an acceptor substance, excellent holeinjection from the first electrode layer 104 can be obtained, whichresults in a reduction in driving voltage of the light-emitting element.Such a composite material can be formed by co-evaporation of a substancehaving a high hole transport property and an acceptor substance. Thehole injection layer 701 is formed using the composite material, wherebyhole injection from the first electrode layer 104 to the EL layer 106 isfacilitated.

As the organic compound for the composite material, any of a variety ofcompounds such as aromatic amine compounds, carbazole derivatives,aromatic hydrocarbons, and high molecular compounds (e.g., oligomers,dendrimers, and polymers) can be used. The organic compound used for thecomposite material is preferably an organic compound having a high holetransport property. Specifically, a substance having a hole mobility of10⁻⁶ cm²/Vs or higher is preferably used. Note that any other substancemay be used as long as the hole transport property thereof is higherthan the electron transport property thereof. Specific examples of theorganic compound that can be used for the composite material are givenbelow.

Examples of the organic compound that can be used for the compositematerial include aromatic amine compounds such as TDATA, MTDATA, DPAB,DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), and4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP),and carbazole compounds such as 4,4′-di(N-carbazolyl)biphenyl(abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene(abbreviation: TCPB), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA),9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

Further, any of the following aromatic hydrocarbon compounds may beused: 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation:t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),9,10-bis[2-(1-naphthyl)phenyl]-2-tert-butylanthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, and the like.

Furthermore, any of the following aromatic hydrocarbon compounds may beused: 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene,pentacene, coronene, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation:DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation:DPVPA), and the like.

Examples of the electron acceptor include organic compounds such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ) and chloranil; and transition metal oxides. Other examplesinclude oxides of metals belonging to Groups 4 to 8 in the periodictable. Specifically, vanadium oxide, niobium oxide, tantalum oxide,chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, andrhenium oxide are preferable because of their high electron acceptingproperty. Among these, molybdenum oxide is particularly preferablebecause it is stable in the air, has a low hygroscopic property, and iseasily handled.

The composite material may be formed using the above electron acceptorand the above high molecular compound such as PVK, PVTPA, PTPDMA, orPoly-TPD and used for the hole injection layer 701.

The hole transport layer 702 is a layer containing a substance having ahigh hole transport property. As the substance having a high holetransport property, any of the following aromatic amine compounds can beused, for example: NPB, TPD, BPAFLP,4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). The substances given here are mainly ones thathave a hole mobility of 10⁻⁶ cm²/Vs or higher. Note that any othersubstance may be used as long as the hole transport property thereof ishigher than the electron transport property thereof. Note that the layercontaining a substance having a high hole transport property is notlimited to a single layer and may be formed of a stack of two or morelayers containing any of the above substances.

For the hole transport layer 702, a carbazole derivative such as CBP,CzPA, or PCzPA or an anthracene derivative such as t-BuDNA, DNA, orDPAnth may be used.

For the hole transport layer 702, a high molecular compound such as PVK,PVTPA, PTPDMA, or Poly-TPD may be used.

The light-emitting layer 703 is a layer containing a light-emittingorganic compound. As the light-emitting organic compound, for example, afluorescent compound which exhibits fluorescence or a phosphorescentcompound which exhibits phosphorescence can be used.

The fluorescent compounds that can be used for the light-emitting layer703 will be given. Examples of a material for blue light emissionincludeN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA), and4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA). Further, examples of a material for green lightemission includeN-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),N-[9,10-bis(1,1′-biphenyl-2-yl)]-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), and N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA). Examples of a material for yellow lightemission include rubrene and5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT).Examples of a material for red light emission include organometalliccomplexes such asbis[2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C^(3′)]iridium(III)acetylacetonate (abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)), and2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP). Examples of a material for red light emissioninclude N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine(abbreviation: p-mPhTD), and7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD).

The phosphorescent compounds that can be used for the light-emittinglayer 703 will be given. Examples of a material for blue light emissionare include bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III) picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)), andbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIr(acac)). Examples of a material forgreen light emission includetris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(ppy)₂(acac)),bis(1,2-diphenyl-1H-benzimidazolato)iridium(III)acetylacetonate(abbreviation: Ir(pbi)₂(acac)),bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation:Ir(bzq)₂(acac)), and tris(benzo[h]quinolinato)iridium(III)(abbreviation: Ir(bzq)₃). Examples of a material for yellow lightemission includebis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis[2-(4′-perfluorophenylphenyl)pyridinato]iridium(III)acetylacetonate(abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(bt)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)-5-methylpyrazinato]iridium(III)(abbreviation: Ir(Fdppr-Me)₂(acac)), and(acetylacetonato)bis{2-(4-methoxyphenyl)-3,5-dimethylpyrazinato}iridium(III)(abbreviation: Ir(dmmoppr)₂(acac)). Examples of a material for orangelight emission include tris(2-phenylquinolinato-N,C^(2′))iridium(III)(abbreviation: Ir(pq)₃),bis(2-phenylquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(pq)₂(acac)),(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-Me)₂(acac)), and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-iPr)₂(acac)). Examples of a material for redlight emission include organometallic complexes such asbis[2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C^(3′)]iridium(III)acetylacetonate(abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)),(dipivaloylmethanato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(dpm)), and2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II)(abbreviation: PtOEP). Further, rare-earth metal complexes, such astris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:Tb(acac)₃(Phen)),tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃(Phen)), andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)), exhibit light emission from rare-earthmetal ions (electron transition between different multiplicities), andthus can be used as phosphorescent compounds.

Note that the light-emitting layer 703 may have a structure in which theabove light-emitting organic compound (a guest material) is dispersed inanother substance (a host material). As a host material, a variety ofkinds of materials can be used, and it is preferable to use a substancewhich has a lowest unoccupied molecular orbital level (LUMO level)higher than that of the light-emitting material and has a highestoccupied molecular orbital level (HOMO level) lower than that of thelight-emitting material.

Specific examples of the host material include metal complexes such astris(8-quinolinolato)aluminum(III) (abbreviation: Alq),tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), andbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ);heterocyclic compounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen), andbathocuproine (abbreviation: BCP); condensed aromatic compounds such as9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA),3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene(abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,9′-bianthryl (abbreviation: BANT),9,9′-(stilbene-3,3′-diyl)diphenanthrene (abbreviation: DPNS),9,9′-(stilbene-4,4′-diyl)diphenanthrene (abbreviation: DPNS2),3,3′,3″-(benzene-1,3,5-triyl)tripyrene (abbreviation: TPB3),9,10-diphenylanthracene (abbreviation: DPAnth), and6,12-dimethoxy-5,11-diphenylchrysene; and aromatic amine compounds suchas N,N-dipheyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine(abbreviation: DPhPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA),N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine(abbreviation: PCAPBA),N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA), NPB (or α-NPD), TPD, DFLDPBi, and BSPB.

As the host material, plural kinds of materials can be used. Forexample, in order to suppress crystallization, a substance such asrubrene which suppresses crystallization may be further added. Inaddition, NPB, Alq, or the like may be further added in order toefficiently transfer energy to a guest material.

When a structure in which a guest material is dispersed in a hostmaterial is employed, crystallization of the light-emitting layer 703can be suppressed. Further, concentration quenching due to highconcentration of the guest material can be suppressed.

For the light-emitting layer 703, a high molecular compound can be used.Specifically, a material for blue light emission, a material for greenlight emission, and a material for orange to red light emission aregiven. Examples of a material for blue light emission includepoly(9,9-dioctylfluorene-2,7-diyl) (abbreviation: PFO),poly[(9,9-dioctylfluorene-2,7-diyl-co-(2,5-dimethoxybenzene-1,4-diyl)](abbreviation: PF-DMOP), andpoly{(9,9-dioctylfluorene-2,7-diyl)-co-[N,N′-di-(p-butylphenyl)-1,4-diaminobenzene]}(abbreviation: TAB-PFH). Examples of a material for green light emissioninclude poly(p-phenylenevinylene) (abbreviation: PPV),poly[(9,9-dihexylfluorene-2,7-diyl)-alt-co-(benzo[2,1,3]thiadiazole-4,7-diyl)](abbreviation:PFBT), andpoly[(9,9-dioctyl-2,7-divinylenfluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)].Examples of a material for orange to red light emission includepoly[2-methoxy-5-(2′-ethylhexoxy)-1,4-phenylenevinylene] (abbreviation:MEH-PPV), poly(3-butylthiophene-2,5-diyl) (abbreviation: R4-PAT),poly{[9,9-dihexyl-2,7-bis(1-cyanovinylene)fluorenylene]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]}, andpoly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-bis(1-cyanovinylenephenylene)]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]}(abbreviation: CN-PPV-DPD).

Note that the light-emitting layer 703 may have a layered structure oftwo or more layers. When the light-emitting layer 703 has a layeredstructure of two or more layers and the kinds of light-emittingsubstances for light-emitting layers vary, a variety of emission colorscan be obtained. In addition, a plurality of light-emitting substancesof different colors is used as the light-emitting substances, wherebylight emission having a broad spectrum or white light emission can alsobe obtained. In particular, for a lighting device in which highluminance is required, a structure in which light-emitting layers arestacked is preferable.

The electron transport layer 704 is a layer containing a substancehaving a high electron transport property. As the substance having ahigh electron transport property, any of the following can be used, forexample: a metal complex having a quinoline skeleton or a benzoquinolineskeleton, such as tris(8-quinolinolato)aluminum (abbreviation: Alq),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂), orbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq). Alternatively, a metal complex or the like including anoxazole-based or thiazole-based ligand, such asbis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂) orbis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)₂),can be used. Other than the metal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like may be used. Thesubstances mentioned here are mainly ones that have an electron mobilityof 10⁻⁶ cm²/V·s or higher. The electron transport layer is notnecessarily a single layer and may be formed of a stack including two ormore layers made of the aforementioned substance.

The electron injection layer 705 is a layer containing a substancehaving a high electron injection property. For the electron injectionlayer 705, an alkali metal, an alkaline earth metal, or a compoundthereof, such as lithium, cesium, calcium, lithium fluoride, cesiumfluoride, calcium fluoride, or lithium oxide, can be used. Further, arare earth metal compound such as erbium fluoride may be used. Asubstance for forming the electron transport layer 704 may be used.

Note that the hole injection layer 701, the hole transport layer 702,the light-emitting layer 703, the electron transport layer 704, and theelectron injection layer 705 which are described above can each beformed by an evaporation method (e.g., a vacuum evaporation method), anink-jet method, a coating method, or the like.

Note that a plurality of EL layers may be stacked between the firstelectrode layer 104 and the second electrode layer 108 as illustrated inFIGS. 8B1 and 8B2. FIG. 8B 1 illustrates an example including two ELlayers, in which a first EL layer 800 and a second EL layer 801 areprovided between the first electrode layer 104 and the second electrodelayer 108, with a charge generation layer 803 laid between the first ELlayer 800 and the second EL layer 801. FIG. 8B2 illustrates an exampleincluding three EL layers, in which the first EL layer 800, the secondEL layer 801, and a third EL layer 802 are provided between the firstelectrode layer 104 and the second electrode layer 108, with chargegeneration layers 803 a and 803 b laid between the first EL layer 800and the second EL layer 801 and between the second EL layer 801 and thethird EL layer 802, respectively.

When the EL layers are stacked, the electron generation layer (theelectron generation layer 803, 803 a, or 803 b) is preferably providedbetween the stacked EL layers (between the first EL layer 800 and thesecond EL layer 801 or between the second EL layer 801 and the third ELlayer 802). The charge generation layers 803, 803 a, and 803 b can eachbe formed using the above composite material. Further, the chargegeneration layers 803, 803 a, and 803 b may each have a layeredstructure including a layer containing the composite material and alayer containing another material. In that case, as the layer containinganother material, a layer containing an electron donating substance anda substance having a high electron transport property, a layer formed ofa transparent conductive film, or the like can be used. As for alight-emitting element having such a structure, problems such as energytransfer and quenching are less likely to occur, and thus alight-emitting element which has both high luminous efficiency and longlifetime can be easily obtained due to expansion in the choice ofmaterials. Moreover, a light-emitting element which providesphosphorescence from one of the EL layers and fluorescence from theother can be readily obtained. Note that this structure can be combinedwith any of the above structures of the EL layer.

When the charge generation layer is provided between the stacked ELlayers as illustrated in FIGS. 8B1 and 8B2, the element can have highluminance and a long lifetime while the current density is kept low. Inaddition, a voltage drop due to resistance of an electrode material canbe reduced, whereby uniform light emission in a large area is possible.

In the case of a stack-type element having a structure in which two ELlayers are stacked, white light emission can be extracted outside byallowing a first EL layer and a second EL layer to emit light ofcomplementary colors. White light emission can also be obtained with astructure including a plurality of light-emitting layers in which lightemission color of a first EL layer and light emission color of a secondEL layer are colors complementary to each other. As complementaryrelations blue and yellow, blue-green and red, and the like can begiven. A substance which emits blue light, yellow light, blue-greenlight, or red light may be selected as appropriate from, for example,the light-emitting substances given above.

An example of a light-emitting element having a structure in which aplurality of EL layers is stacked will be described below. First, anexample of a structure in which each of the first EL layer and thesecond EL layer includes a plurality of light-emitting layers which emitlight of complementary colors will be described. With this structure,white light emission can be obtained.

For example, the first EL layer includes a first light-emitting layerwhich has an emission spectrum with a peak in the wavelength range ofblue to blue-green, and a second light-emitting layer which has anemission spectrum with a peak in the wavelength range of yellow toorange. The second EL layer includes a third light-emitting layer whichhas an emission spectrum with a peak in the wavelength range ofblue-green to green, and a fourth light-emitting layer which has anemission spectrum with a peak in the wavelength range of orange to red.

In this case, light emission from the first EL layer is a combination oflight emission from both the first light-emitting layer and the secondlight-emitting layer and thus exhibits an emission spectrum having botha peak in the wavelength range of blue to blue-green and a peak in thewavelength range of yellow to orange. That is, the first EL layer emitslight of two-wavelength type white or a two-wavelength type color closeto white.

In addition, light emission from the second EL layer is a combination oflight emission from both the third light-emitting layer and the fourthlight-emitting layer and thus exhibits an emission spectrum having botha peak in the wavelength range of blue-green to green and a peak in thewavelength range of orange to red. That is, the second EL layer emitslight of two-wavelength type white color or a two-wavelength type colorclose to white, which is different from that of the first EL layer.

Accordingly, by combining the light emission from the first EL layer andthe light emission from the second EL layer, white light emission whichcovers the wavelength range of blue to blue-green, the wavelength rangeof blue-green to green, the wavelength range of yellow to orange, andthe wavelength range of orange to red can be obtained.

Further, the wavelength range of yellow to orange (greater than or equalto 560 nm and less than 580 nm) is a wavelength range of high spectralluminous efficacy; thus, application of an EL layer which includes alight-emitting layer having an emission spectrum peak in the wavelengthrange of yellow to orange is useful. For example, a structure can beused in which a first EL layer which includes a light-emitting layerhaving an emission spectrum peak in a blue wavelength range, a second ELlayer which includes a light-emitting layer having an emission spectrumpeak in an yellow wavelength range, and a third EL layer which includesa light-emitting layer having an emission spectrum peak in a redwavelength range are stacked.

Further, two or more EL layers exhibiting yellow to orange color may bestacked. The power efficiency can be further improved by stacking two ormore EL layers exhibiting yellow to orange color.

For example, in the case of a light-emitting element in which three ELlayers are stacked as in FIG. 8B1, a second EL layer and a third ELlayer each of which includes a light-emitting layer having an emissionspectrum peak in yellow to orange wavelength range may be stacked over afirst EL layer which includes a light-emitting layer having an emissionspectrum peak in a blue wavelength range (greater than or equal to 400nm and less than 480 nm). Note that the wavelengths of the peaks of thespectra of light emitted from the second EL layer and the third EL layermay be the same or different from each other.

When the number of EL layers which are stacked is increased, the powerefficiency of a light-emitting element can be improved; however, thereoccurs a problem that the manufacturing process becomes complicated.Thus, the structure in which three EL layers are stacked as in FIG. 8B2is preferable because the power efficiency is high as compared to thecase of a structure of two EL layers and the manufacturing process issimple as compared to the case of a structure of four or more EL layers.

The use of the EL layer which has an emission spectrum peak in theyellow to orange wavelength range makes it possible to utilize thewavelength range of high spectral luminous efficacy, allowingimprovement in power efficiency. Accordingly, the power efficiency ofthe whole light-emitting element can be improved. Such a structure isadvantageous in terms of spectral luminous efficacy and thus enablesimprovement in power efficiency as compared to the case where, forexample, an EL layer which emits green light and an EL layer which emitsred light are stacked to obtain a light-emitting element which emitsyellow to orange light. Further, the emission intensity of light of theblue wavelength range of low spectral luminous efficacy is relativelylow as compared to the case of using one EL layer which has an emissionspectrum peak in the yellow to orange wavelength range of high spectralluminous efficacy; thus, the color of emitted light is close toincandescent color (or warm white), and the power efficiency isimproved.

In other words, in the above light-emitting element, the color of lightwhich is obtained by combining light whose emission spectrum peak is inthe yellow to orange wavelength range and whose wavelength of the peakis greater than or equal to 560 nm and less than 580 nm and light whoseemission spectrum peak is in the blue wavelength range (i.e., the colorof light emitted from the light-emitting element) can be natural colorlike warm white or incandescent color. In particular, incandescent colorcan be easily achieved.

As a light-emitting substance which emits light having a peak in theyellow to orange wavelength range, for example, an organometalliccomplex in which a pyrazine derivative functions as a ligand can beused. Alternatively, the light-emitting layer may be formed bydispersing a light-emitting substance (a guest material) in anothersubstance (a host material). A phosphorescent compound can be used asthe light-emitting substance which emits light having a peak in theyellow to orange wavelength range. The power efficiency in the case ofusing a phosphorescent compound is three to four times as high as thatin the case of using a fluorescent compound. The above organometalliccomplex in which a pyrazine derivative functions as a ligand is aphosphorescent compound, has high emission efficiency, and easily emitslight in the yellow to orange wavelength range, and thus is favorable.

As a light-emitting substance which emits light having a peak in theblue wavelength range, for example, a pyrene diamine derivative can beused. A fluorescent compound can be used as the light-emitting substancewhich emits light having a peak in the blue wavelength range. The use ofa fluorescent compound makes it possible to obtain a light-emittingelement which has a longer lifetime than a light-emitting element inwhich a phosphorescent compound is used. The above pyrene diaminederivative is a fluorescent compound, can obtain an extremely highquantum yield, and has a long lifetime; thus, the above pyrene diaminederivative is favorable.

As illustrated in FIG. 8C, the EL layer may include the hole injectionlayer 701, the hole transport layer 702, the light-emitting layer 703,the electron transport layer 704, an electron injection buffer layer706, an electron relay layer 707, and a composite material layer 708which is in contact with the second electrode layer 108, between thefirst electrode layer 104 and the second electrode layer 108.

It is preferable to provide the composite material layer 708 which is incontact with the second electrode layer 108 because damage caused to theEL layer 106 particularly when the second electrode layer 108 is formedby a sputtering method can be reduced. The composite material layer 708can be formed using the above composite material in which an organiccompound having a high hole transport property is mixed with an acceptorsubstance.

Further, by providing the electron injection buffer layer 706, aninjection barrier between the composite material layer 708 and theelectron transport layer 704 can be reduced; thus, electrons generatedin the composite material layer 708 can be easily injected to theelectron transport layer 704.

Any of the following substances having high electron injectionproperties can be used for the electron injection buffer layer 706: analkali metal, an alkaline earth metal, a rare earth metal, a compound ofthe above metal (e.g., an alkali metal compound (e.g., an oxide such aslithium oxide, a halide, and carbonate such as lithium carbonate orcesium carbonate), an alkaline earth metal compound (e.g., an oxide, ahalide, and carbonate), a rare earth metal compound (e.g., an oxide, ahalide, and carbonate), and the like.

Further, in the case where the electron injection buffer layer 706contains a substance having a high electron transport property and adonor substance, the donor substance is preferably added so that themass ratio of the donor substance to the substance having a highelectron transport property is from 0.001:1 to 0.1:1. Note that as thedonor substance, an organic compound such as tetrathianaphthacene(abbreviation: TTN), nickelocene, or decamethylnickelocene may be usedas well as an alkali metal, an alkaline earth metal, a rare earth metal,a compound of the above metal (e.g., an alkali metal compound (e.g., anoxide such as lithium oxide, a halide, and carbonate such as lithiumcarbonate or cesium carbonate), an alkaline earth metal compound (e.g.,an oxide, a halide, and carbonate), and a rare earth metal compound(e.g., an oxide, a halide, and carbonate). Note that as the substancehaving a high electron transport property, a material similar to thematerial for the electron transport layer 704 described above can beused.

Furthermore, the electron relay layer 707 is preferably formed betweenthe electron injection buffer layer 706 and the composite material layer708. The electron relay layer 707 is not necessarily provided; however,by providing the electron relay layer 707 having a high electrontransport property, electrons can be rapidly transported to the electroninjection buffer layer 706.

The structure in which the electron relay layer 707 is sandwichedbetween the composite material layer 708 and the electron injectionbuffer layer 706 is a structure in which the acceptor substancecontained in the composite material layer 708 and the donor substancecontained in the electron injection buffer layer 706 are less likely tointeract with each other, and thus their functions hardly interfere witheach other. Accordingly, an increase in driving voltage can beprevented.

The electron relay layer 707 contains a substance having a high electrontransport property and is formed so that the LUMO level of the substancehaving a high electron transport property is located between the LUMOlevel of the acceptor substance contained in the composite materiallayer 708 and the LUMO level of the substance having a high electrontransport property contained in the electron transport layer 704. In thecase where the electron relay layer 707 contains a donor substance, thedonor level of the donor substance is controlled so as to be locatedbetween the LUMO level of the acceptor substance in the compositematerial layer 708 and the LUMO level of the substance having a highelectron transport property contained in the electron transport layer704. As a specific value of the energy level, the LUMO level of thesubstance having a high electron transport property contained in theelectron relay layer 707 is preferably greater than or equal to −5.0 eV,more preferably greater than or equal to −5.0 eV and less than or equalto −3.0 eV.

As the substance having a high electron transport property contained inthe electron relay layer 707, a phthalocyanine-based material or a metalcomplex having a metal-oxygen bond and an aromatic ligand is preferablyused.

As the phthalocyanine-based material contained in the electron relaylayer 707, specifically, any of the following is preferably used: CuPc,a phthalocyanine tin(II) complex (SnPc), a phthalocyanine zinc complex(ZnPc), cobalt(II) phthalocyanine, β-form (CoPc), phthalocyanine iron(FePc), and vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine(PhO-VOPc).

As the metal complex having a metal-oxygen bond and an aromatic ligand,which is contained in the electron relay layer 707, a metal complexhaving a metal-oxygen double bond is preferably used. The metal-oxygendouble bond has an acceptor property (a property of easily acceptingelectrons); thus, electrons can be transferred (donated and accepted)more easily. Further, the metal complex which has a metal-oxygen doublebond is considered stable. Thus, the use of the metal complex having ametal-oxygen double bond makes it possible to drive the light-emittingelement at low voltage more stably.

As the metal complex having a metal-oxygen bond and an aromatic ligand,a phthalocyanine-based material is preferable. Specifically, any ofvanadyl phthalocyanine (VOPc), a phthalocyanine tin(IV) oxide complex(SnOPc), and a phthalocyanine titanium oxide complex (TiOPc) ispreferable because a metal-oxygen double bond is more likely to act onanother molecular in terms of a molecular structure and an acceptorproperty is high.

Note that as the phthalocyanine-based material described above, aphthalocyanine-based material having a phenoxy group is preferable.Specifically, a phthalocyanine derivative having a phenoxy group, suchas PhO-VOPc, is preferable. A phthalocyanine derivative having a phenoxygroup is soluble in a solvent; thus, the phthalocyanine derivative hasan advantage of being easily handled during formation of alight-emitting element and an advantage of facilitating maintenance ofan apparatus used for film formation.

The electron relay layer 707 may further contain a donor substance.Examples of the donor substance include organic compounds such astetrathianaphthacene (abbreviation: TTN), nickelocene, anddecamethylnickelocene, in addition to an alkali metal, an alkaline earthmetal, a rare earth metal, and compounds of the above metals (e.g.,alkali metal compounds (including an oxide such as lithium oxide, ahalide, and carbonates such as lithium carbonate and cesium carbonate),alkaline earth metal compounds (including an oxide, a halide, and acarbonate), and rare earth metal compounds (including an oxide, ahalide, and a carbonate)). When such a donor substance is contained inthe electron relay layer 707, electrons can be transferred easily andthe light-emitting element can be driven at lower voltage.

In the case where a donor substance is contained in the electron relaylayer 707, other than the materials described above as the substancehaving a high electron transport property, a substance having a LUMOlevel greater than the acceptor level of the acceptor substancecontained in the composite material layer 708 may be used. As a specificenergy level of the substance having a LUMO level, a LUMO level isgreater than or equal to −5.0 eV, preferably greater than or equal to−5.0 eV and less than or equal to −3.0 eV. As examples of such asubstance, a perylene derivative and a nitrogen-containing condensedaromatic compound can be given. Note that a nitrogen-containingcondensed aromatic compound is preferably used for the electron relaylayer 707 because of its stability.

As specific examples of the perylene derivative, the following can begiven: 3,4,9,10-perylenetetracarboxylicdianhydride (abbreviation:PTCDA), 3,4,9,10-perylenetetracarboxylic-bis-benzimidazole(abbreviation: PTCBI), N,N′-dioctyl-3,4,9,10-perylenetetracarboxylicdiimide (abbreviation: PTCDI-C8H), andN,N′-dihexyl-3,4,9,10-perylenetetracarboxylic diimide (Hex PTC).

As specific examples of the nitrogen-containing condensed aromaticcompound, the following can be given:pirazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (PPDN),2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT(CN)₆),2,3-diphenylpyrido[2,3-b]pyrazine (2PYPR), and2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine (F2PYPR).

Other examples are 7,7,8,8-tetracyanoquinodimethane (abbreviation:TCNQ), 1,4,5,8-naphthalenetetracarboxylicdianhydride (abbreviation:NTCDA), perfluoropentacene, copper hexadecafluoro phthalocyanine(abbreviation: F₁₆CuPc),N,N′-bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl-1,4,5,8-naphthalenetetracarboxylicdiimide (abbreviation: NTCDI-C8F),3′,4′-dibutyl-5,5″-bis(dicyanomethylene)-5,5″-dihydro-2,2′:5′,2″terthiophen(abbreviation: DCMT), and methanofullerene (e.g., [6,6]-phenyl C₆₁butyric acid methyl ester).

Note that in the case where a donor substance is contained in theelectron relay layer 707, the electron relay layer 707 may be formed bya method such as co-evaporation of the substance having a high electrontransport property and the donor substance.

The hole injection layer 701, the hole transport layer 702, thelight-emitting layer 703, and the electron transport layer 704 may eachbe formed using any of the above materials.

Then, the second electrode layer 108 is formed over the EL layer 106.

The second electrode layer 108 is provided on the side opposite to theside from which light is extracted and is formed using a reflectivematerial. As the reflective material, a metal material such as aluminum,gold, platinum, silver, nickel, tungsten, chromium, molybdenum, iron,cobalt, copper, or palladium can be used. Alternatively, any of thefollowing may be used: alloys containing aluminum (aluminum alloys) suchas an alloy of aluminum and titanium, an alloy of aluminum and nickel,and an alloy of aluminum and neodymium; and an alloy containing silver,such as an alloy of silver and copper. An alloy of silver and copper ispreferable because of its high heat resistance. Further, a metal film ora metal oxide film is stacked in contact with an aluminum alloy film,whereby oxidation of the aluminum alloy film can be suppressed. Asexamples of a material of the metal film or the metal oxide film,titanium and titanium oxide are given. The above materials arepreferable because they are present in large amounts in the Earth'scrust and inexpensive and thus a reduction in manufacturing cost of alight-emitting element can be achieved.

Note that this embodiment can be freely combined with any of the otherembodiments as appropriate.

Embodiment 3

In this embodiment, application examples of a lighting device will bedescribed.

FIG. 9 illustrates an example in which the lighting device according toone embodiment of the present invention is used as an indoor lightingdevice. The lighting device according to one embodiment of the presentinvention can be used not only as a ceiling-mounted lighting device 8202but also as a wall-mounted lighting device 8204 and a floor-mountedlighting device 8205. When the lighting device according to oneembodiment of the present invention is used as the floor-mountedlighting device 8205, a second housing of the floor-mounted lightingdevice 8205 is loaded with the people and objects; therefore, asubstrate and a sealing structure which can sustain the weight of thepeople and the objects which are loaded on the second housing of thefloor-mounted lighting device 8205. In the case where a fragile glasssubstrate is used for the second housing of the floor-mounted lightingdevice 8205, the glass substrate may be protected by providing over theglass substrate a thick plastic plate which has a light-transmittingproperty and can sustain the weight of people and objects which areloaded thereon. Further, since the lighting device according to oneembodiment of the present invention can be reduced in thickness andincreased in size, it is also possible that a wall surface itself servesas a light source like lighting devices 8203 so that a room isilluminated.

The lighting device according to one embodiment of the presentinvention, which has a surface light source, is preferably used as anindoor lighting device because it has advantages such as a reduction innumber of components such as a light-reflecting plate as compared withthe case of using a point light source, or less heat generation ascompared with a filament bulb. Further, the lighting device as a wholeis thin and lightweight; thus, the lighting device can be mounted on avariety of places.

Next, an example in which the lighting device according to oneembodiment of the present invention is applied to an emergency exitlight is illustrated in FIG. 10.

FIG. 10 illustrates an example of the appearance of an emergency exitlight. An emergency exit light 8232 can be formed by combination of thelighting device and a fluorescent plate provided with a fluorescentportion. Alternatively, the emergency exit light 8232 may be formed bycombination of a lighting device which emits light of a specific colorand a light-blocking plate provided with a transmissive portion with ashape illustrated in the drawing. The lighting device according to oneembodiment of the present invention can emit light with a constantluminance, and thus is preferably used as an emergency exit light thatneeds to be on at all times.

The lighting device according to one embodiment of the present inventioncan be thin and lightweight and have a large area and high reliability.

Note that what is described in this embodiment with reference to eachdrawing can be freely combined with or replaced with what is describedin any of the other embodiments as appropriate.

This application is based on Japanese Patent Application serial no.2010-288677 filed with the Japan Patent Office on Dec. 24, 2010, theentire contents of which are hereby incorporated by reference.

What is claimed is:
 1. A lighting device comprising: a light emittingelement comprising: a first electrode comprising a transparentconductive material; a second electrode comprising metal; a layerbetween the first electrode and the second electrode, the layercomprising an organic light-emitting material; and an insulating layerover the first electrode and under the layer, the insulating layerhaving an opening; a first conductive layer electrically connected tothe first electrode through a second conductive layer, wherein the firstconductive layer comprises metal and the second conductive layercomprises an alloy; and a third conductive layer electrically connectedto the second electrode, the third conductive layer having a comb-likeshape, wherein the insulating layer overlaps with the first conductivelayer and the third conductive layer.
 2. The lighting device accordingto claim 1, wherein a resistivity of the first conductive layer is lowerthan a resistivity of the first electrode.
 3. The lighting deviceaccording to claim 1, wherein the second conductive layer has a narrowerwidth than the first conductive layer.
 4. The lighting device accordingto claim 1, wherein the second conductive layer is thinner than thefirst conductive layer.
 5. The lighting device according to claim 1,wherein the metal comprised in the first conductive layer is aluminum,and wherein the alloy comprised in the second conductive layer is analloy comprising molybdenum.
 6. The lighting device according to claim1, wherein the layer overlaps with the opening of the insulating layer.7. The lighting device according to claim 1, wherein the firstconductive layer is over and in contact with a surface, and wherein thethird conductive layer is over and in contact with the surface.
 8. Thelighting device according to claim 1, wherein the insulating layercomprises an organic insulating material.
 9. The lighting deviceaccording to claim 1, wherein the transparent conductive materialcomprised in the first electrode is indium tin oxide.
 10. A lightingdevice comprising: a first electrode comprising a transparent conductivematerial; an insulating layer over the first electrode, the insulatinglayer having an opening; a layer over the first electrode and theinsulating layer, the layer comprising an organic light-emittingmaterial; a second electrode over the layer, the second electrodecomprising metal; a first conductive layer electrically connected to thefirst electrode through a second conductive layer, wherein the firstconductive layer comprises metal and the second conductive layercomprises an alloy; and a third conductive layer electrically connectedto the second electrode, the third conductive layer having a comb-likeshape, wherein the insulating layer overlaps with the first conductivelayer and the third conductive layer.
 11. The lighting device accordingto claim 10, wherein a resistivity of the first conductive layer islower than a resistivity of the first electrode.
 12. The lighting deviceaccording to claim 10, wherein the second conductive layer has anarrower width than the first conductive layer.
 13. The lighting deviceaccording to claim 10, wherein the second conductive layer is thinnerthan the first conductive layer.
 14. The lighting device according toclaim 10, wherein the metal comprised in the first conductive layer isaluminum, and wherein the alloy comprised in the second conductive layeris an alloy comprising molybdenum.
 15. The lighting device according toclaim 10, wherein the layer overlaps with the opening of the insulatinglayer.
 16. The lighting device according to claim 10, wherein the firstconductive layer is over and in contact with a surface, and wherein thethird conductive layer is over and in contact with the surface.
 17. Thelighting device according to claim 10, wherein the insulating layercomprises an organic insulating material.
 18. The lighting deviceaccording to claim 10, wherein the transparent conductive materialcomprised in the first electrode is indium tin oxide.